Field of the Invention
The present invention relates to a method of constructing a three-dimensional (3D) image, image processor, and electron microscope.
Description of Related Art
Electron tomography (ET) has been known as a technique for observing and analyzing the morphology of a sample in a three-dimensional manner by applying a computerized tomography (CT) method to an electron microscope such as a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM) (see, for example, JP-A-2012-209050).
In recent years, EDS tomography that is a combination of energy dispersive X-ray spectroscopy (EDS) and electron tomography (ET) has attracted attention. EDS tomography is a method of three-dimensional elemental analysis in which EDS and ET are combined.
A process of EDS tomography starts with acquiring elemental mapping images by tilting a sample at various angles using an electron microscope. For example, the angular range of tilt is set to ±60 degrees, and the sample is tilted in increments of 5 degrees. If an elemental mapping image is acquired at each tilt angle, then a series of tilted images consisting of 25 elemental mapping images can be obtained. Then, computer tomography is applied to the elemental mapping images constituting the series of tilted images, thus obtaining two-dimensional reconstructed cross-sectional images. A three-dimensional image showing a three-dimensional elemental distribution is derived by superimposing the resulting, series of cross-sectional images.
Generally, when a sample is to be observed in an electron microscope, the sample is held on a mesh having a diameter of 3 mm. If the sample is tilted in increments in an attempt to obtain a series of tilted images, the EDS detector is hidden in a shadow of the frame of the sample holder, mesh, or sample at a certain tilt angle. Consequently, characteristic X-rays produced from the sample are cut off, decreasing the X-ray intensity. Also, the brightness levels of elemental mapping images decrease. These present the problem that the accuracy of three-dimensional images will deteriorate.